1. Field of the Invention
This invention relates to a capacitive pressure sensor including an upper electrode with a diaphragm structure and a lower electrode facing the upper electrode with a gap therebetween for detecting a pressure.
2. Description of the Prior Art
Capacitive pressure sensors having an upper electrode with a diaphragm structure and a lower electrode facing the upper electrode with a gap therebetween for detecting a pressure are known. Japanese patent application provisional publication No. 9-257618 and Japanese patent No. 2000-22172 disclose pressure sensors having the diaphragm structure for detecting a pressure from variation in capacitance between the upper and lower electrodes, wherein the upper electrode is bendable due to the diaphragm structure by the pressure applied thereto. In these pressure sensors, it is desirable to provide a diagnostic operation.
An object of the present invention is to provide a superior capacitive pressure sensor.
A related object is to provide a superior capacitive pressure sensor with dual pressure sensor structure usable for diagnostic.
According to the present invention, there is provided a capacitive pressure sensor with a dual pressure sensor structure, wherein the pressure in a first cavity space of one pressure sensor between an upper electrode as a diaphragm and a lower electrode, is equalized to the pressure in a second cavity space by a fluid communication structure therebetween.
According to the present invention, a first aspect of the present invention provides a capacitive pressure sensor including: a substrate; a first capacitive portion including a first lower electrode on a surface of the substrate and a first upper electrode facing the first lower electrode with a first cavity space, the first upper electrode being supportable by the substrate to have a first diaphragm structure; a second capacitive portion including a second lower electrode on the surface of the substrate and a second upper electrode facing the second lower electrode with a second cavity space, the second upper electrode being supportable by the substrate to have a second diaphragm structure; and a communicating structure for providing fluid communication between the first and second cavity spaces.
According to the present invention, a second aspect of the present invention provides the capacitive pressure sensor based on the first aspect, further including comparing means for comparing a first value from the first capacitive portion representing a pressure applied thereto with a second value from the second capacitive portion representing the pressure applied thereto to output a diagnostic result.
According to the present invention, a third aspect of the present invention provides the capacitive pressure sensor based on the first aspect, wherein the first capacitive portion has a first layer structure with the first upper and lower electrodes in a sectional elevation view of the capacitive pressure sensor perpendicular to the surface of the substrate, and the second capacitive portion has a second layer structure with the second upper and lower electrodes in the sectional elevation view, and the first layer structure is substantially the same as the second layer structure, and wherein the first and second upper electrodes have first and second areas in parallel to the surface of the substrate, respectively, and the first area is different from the second area.
According to the present invention, a fourth aspect of the present invention provides the capacitive pressure sensor based on the first aspect, wherein the second capacitive portion is arranged to surround the first capacitive portion, the first upper electrode, at an outer circumference, is connected to the second upper electrode at an inner circumference, and the first cavity space is connected to the second cavity space.
According to the present invention, a fifth aspect of the present invention provides the capacitive pressure sensor based on the fourth aspect, further includes a supporting member between the first and second upper electrodes to support the outer circumference of the first upper electrode and the inner circumference of the second upper electrode and also to suppress position variation of the second upper electrode. The communication structure is formed in said the supporting member.